Sigma Boötis is a single,[15][16] yellow-huedstar in the northernconstellation ofBoötes. Its name is aBayer designation that isLatinized from σ Boötis, and abbreviated Sigma Boo or σ Boo. This star is visible to thenaked eye with anapparent visual magnitude of 4.46.[2] Located to the southeast ofRho Boötis, the dwarf Sigma may at first appear as a naked-eye double, but the angular proximity with Rho is merely line-of-sight. Sigma Boötis is located at a distance of 51.4light-years (16 pc) from theSun based onparallax.[17] The star has a relatively highproper motion and is traversing the sky at the rate of0.230″ yr−1.[18]
Thestellar classification of Sigma Boötis is F4VkF2mF1.[3] This notation is used for so-called "metal-weak" stars;Am stars withabsorption lines of some metals weaker than expected in comparison with otherspectral features. The 'F4V', indicating anF-type main-sequence star, is derived from the hydrogen spectral lines and the shape of the metallic lines, the 'kF2' means it has theCalcium K line strength of a hotter F2 star and 'mF1' showing it has themetallic line strength of an F1 star.[19] It is around twice as luminous as a comparablezero age main sequence star, which may indicate it is near the end of itsmain sequence lifetime.[13]
Sigma Boötis is a solar-type star but is larger and more massive than the Sun. It has an estimated age of around two[12] to three[13] billion years and is spinning with aprojected rotational velocity of 7 km/s.[11] There is some evidence of variation inradial velocity as well as rotational modulation of active latitudes.[13] Even though the outer convective zone of the star only occupies a few percent of the stellar radius, a surfacemagnetic field has been detected with a strength of1.4±0.4 Gauss.[20] This surface field forms a relatively simpledipole topology.[21] The star is radiating 3.5[9] times the luminosity of the Sun from itsphotosphere at aneffective temperature of 6,594 K.[9] It appears to be a source forX-ray emission.[22]
Sigma Boötis is known by several different names, including σ Boo, 28 Boötis, BD+30°2536, GC 19659, GJ 557, HD 128167, HIP 71284, HR 5447, SAO 83416, and CCDM 14347+2945.[14]
InChinese,梗河 (Gěng Hé), meaningCelestial Lance, refers to an asterism consisting of σ Boötis,ε Boötis andρ Boötis.[24] Consequently, theChinese name for σ Boötis itself is梗河二 (Gěng Hé èr, English:the Second Star of Celestial Lance.)[25]
^abGray, R. O.; et al. (April 2001), "The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. I. Precise Spectral Types for 372 Stars",The Astronomical Journal,121 (4):2148–2158,Bibcode:2001AJ....121.2148G,doi:10.1086/319956.
^David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets",The Astrophysical Journal,804 (2): 146,arXiv:1501.03154,Bibcode:2015ApJ...804..146D,doi:10.1088/0004-637X/804/2/146,S2CID33401607.
^Seach, J. M.; et al. (July 2022), "The magnetic fields of β Coronae Borealis and the early F-star σ Bootis",Monthly Notices of the Royal Astronomical Society,513 (3):4278–4294,Bibcode:2022MNRAS.513.4278S,doi:10.1093/mnras/stac1173.
^Haakonsen, Christian Bernt; Rutledge, Robert E. (September 2009), "XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources",The Astrophysical Journal Supplement,184 (1):138–151,arXiv:0910.3229,Bibcode:2009ApJS..184..138H,doi:10.1088/0067-0049/184/1/138,S2CID119267456.
